A variety of methods have been used to treat and remove contaminants from water and wastewater. The procedures and techniques actually used by municipal utilities for the treatment of drinking water and sanitary sewage have remained largely unchanged for at least 40 years.
Municipal drinking water treatment typically involves pumping surface (river or reservoir) water to a high energy mixing tank where alum and/or lime is added. The water then flows into a low energy mixing tank where chemically bound sediment floc is formed. From the flocculation tank the water flows into a gravity clarification tank, then on to a granular media filter and finally the water is disinfected with chlorine prior to distribution.
Municipal treatment of groundwater (wells) tends typically to involve the addition of a strong oxidant such as chlorine or potassium permanganate to oxidize a variety of dissolved pollutants such as iron, manganese, trace organics, heavy metals, radionuclides and bacteria. The chemically treated groundwater is then filtered and disinfected prior to distribution.
Municipal treatment of sanitary sewage typically includes screening to remove large solids, treatment of dissolved organics through a process generically referred to as activated sludge, gravity settling (clarification), then filtration and finally disinfection. In the past chlorine was commonly used for the disinfection of both water and wastewater, but as a result of recognition by the US EPA that byproducts of chlorine may be potentially carcinogenic, new regulations have been passed limiting the widespread use of chlorine and requiring the reduction or elimination of disinfection byproducts. Consequently, ultraviolet light has emerged as the disinfectant of choice.
Because procedures and techniques for treating water and wastewater have advanced little over the past 40 years, there is a glaring need for new methods and systems for treating water and wastewater that is efficient, effective and reliable and which produces minimal waste byproducts (sludge).
Prior art attempts to improve systems and electrochemical treatment methods for wastewater treatment have not been satisfactory. Those reported in the literature have utilized either parallel electrified plates made of iron or aluminum as electrodes, or a single rod within a cylinder made of iron or aluminum as electrodes. In the case of the parallel plates, the electrical charge density on the plates is insufficient to properly treat the water or wastewater unless the plate spacing is minimal (less than ¼″; 0.365 cm). This typically results in rapid plugging or clogging of the treatment unit. In the case of a single rod within a cylinder, often the spacing between the central rod and the perimeter wall is so great as to be ineffective in creating a sufficiently strong charge density to completely treat water or wastewater.
Classically, the efforts of the past have focused on the use of either parallel plates or center rods inside a tube as the positively and negatively charged electrodes. Due to the inefficiency of the plate designs, it was considered necessary to minimize plate spacings which quickly resulted in fouling of treatment units. The center rod and tube designs experienced similar problems and attempted to use high voltage potentials to overcome ineffectiveness. In one approach, using electrochemical cells in series with varying electrode materials was tried to achieve the desired treatment effectiveness. In every case, treatment technologies proved to be physically self-limiting and scaling factors (enlarging the units) became problematic. Furthermore, these approaches were typically characterized by high energy consumption as attempts to reach intended treatment levels were explored. This fact became a significant barrier to practical commercialization. Previous attempts to develop effective electrochemical technologies for treatment of water and wastewater resulted in processes that were very expensive to operate and not effective.